This invention relates generally to the field of semiconductor devices and more particularly to a system and method for dynamically regulating a step down power supply.
Modern electronic equipment such as televisions, telephones, radios and computers are generally constructed of solid state devices. Integrated circuits are preferred in electronic equipment because they are extremely small and relatively inexpensive. Additionally, integrated circuits are very reliable because they have no moving parts but are based on the movement of charge carriers.
Integrated circuits may include transistors, capacitors, resistors and other semiconductor devices. Typically, such devices are fabricated on a substrate and interconnected to form power supplies, memory arrays, logic structures, timers and other components of an integrated circuit. One type of power supply is a step down power supply which is operable to receive an input voltage and step down the input voltage to a specified output voltage.
Conventional step down power supplies include high gain, such as 60 to 80 dB, feedback compensation. High gain feedback compensation generally provides good line regulation and initial accuracy for the step down power supply. However, high gain feedback compensation typically uses up to seven feedback components, including resistors and capacitors. The capacitors may be too large for integration into the step down power supply. Thus, typical step down power supplies using high gain feedback compensation have the feedback components external to the step down integrated circuit. In addition, the transient response associated with high gain feedback compensation is limited due to the dominant pole in the feedback network.
Low gain, such as less than 40 dB, feedback compensation may be used to reduce the number of feedback components, which may also allow integration into the step down integrated circuit. Also, the transient response is not limited by a pole for a typical low gain feedback compensation. However, poor line regulation generally results from low gain feedback compensation for a step down power supply. Furthermore, typical step down power supplies with low gain feedback compensation have initial accuracy errors and burden the designer with solving this problem by having the customer select the resistor values to correct the errors.
In accordance with the present invention, a system and method for dynamically regulating a step down power supply are provided that substantially eliminate or reduce disadvantages and problems associated with previously developed systems and methods. In a particular embodiment, low gain feedback compensation is provided in a step down power supply with initial accuracy errors minimized and with relatively good line regulation, which is accomplished by introducing an offset voltage.
According to one embodiment of the present invention, a low gain feedback compensation circuit is provided on an integrated circuit. The feedback compensation circuit is coupled to a step down power supply on the integrated circuit. The step down power supply is operable to receive an input voltage and to generate an output voltage based on the input voltage. The feedback compensation circuit includes a line regulation circuit. The line regulation circuit is operable to receive the input voltage and a reference voltage. The line regulation circuit is also operable to generate an offset voltage based on the input voltage and the reference voltage.
According to another embodiment of the present invention, a method for dynamically regulating an output voltage for a step down power supply is provided. The method includes providing a reference voltage to an error amplifier for a low gain feedback compensation circuit. The feedback compensation circuit includes a line regulation circuit. The reference voltage is received at the line regulation circuit. A first input voltage is received at the line regulation circuit. A first offset voltage is provided to the error amplifier based on the first input voltage and the reference voltage. A second input voltage is received at the line regulation circuit. The second input voltage is different from the first input voltage. A second offset voltage is provided to the error amplifier based on the second input voltage and the reference voltage.
Technical advantages of one or more embodiments of the present invention include providing an improved system for dynamically regulating a step down power supply. In a particular embodiment, a current source provides an offset voltage that is a function of the input voltage and the desired output voltage. As a result, the line regulation is improved and initial accuracy errors are minimized.
Other technical advantages of one or more embodiments of the present invention include integrating a feedback compensation circuit that includes a line regulation circuit into a step down integrated circuit. Accordingly, available die area is increased. In addition, the number of components and the output voltage error due to line voltage changes are minimized.
Technical advantages of one or more embodiments of the present invention also include providing a feedback compensation circuit that has only resistors. As a result, capacitors for the feedback compensation circuit do not need to be integrated into the step down integrated circuit.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims.